Among the several types of sonar systems used to detect underwater objects such as submarines there are several types in which passive hydrophones are deployed or are used in towed arrays in large numbers in a given area and in some means is required to insonify the adjacent volume of water so that it echoes or reflection from such underwater objects are received at the sonobuoys.
Most towed array hydrophones sometimes called long line hydrophones have suffered from interference from flow noise and other interference from water flow and other similar interferences that has prevented towed arrays of long line hydrophones from being very effective in detection of underwater sounds.
It is also well known in the prior art that towed arrays of lone line hydrophones have poor low frequency response. That is to say there are numerous in long line hydrophones used in the prior art there are numerous standing wave problems. Standing waves are reflected back and forth in the long tubular element, in the prior art and therefore tend to set up nodes that interfere with the standing waves and sound waves from the objects submarines or other deep sea objects that generate sound waves. Therefore prior art has been subject to numerous low frequency problems primary from interference from standing waves and other sound waves generated or reflected within the long tubular element of the towed array.
In addition, presently the prior art arrays that are towed behind ships for the purpose of detecting sounds from the depths of the ocean are very sensitive to deep water depths and have a tendency to collapse or otherwise be physically distorted by use in water exceeding 40 feet in depth. Therefore it should be apparent to one skilled in the art that prior art devices have proved to be overly sensitive to the physical parameters of deep water for use in deep water.
In addition to the poor low frequency response of the prior art hydrophones most of such hydrophones are very fragile at depths in excess of 100 feet.
Most of the towed arrays are extremely fragile being made of lightweight metal, plastics and other similar materials. Part of the fragility problem relates to the fact that most long line hydrophones that make up towed arrays are hollow. The reason that the presently used prior art towed arrays are hollow are that when the towed arrays are filled with any particular liquid material there sensitivity is greatly reduced and noise interference is much greater. Therefore from the review of the prior art deficiencies it is clear that there is a needed for a towed array that can accomplish the desired insonification for a limited period of time enough to be launched into the ocean from an aircraft which ones mission is completed, can be towed behind a ship as a long line hydrophone to detect and measure ocean noises.